Putting new water nipples on the pump and manifold (aluminum). Do you use anthing for a sealant...teflon tape, pipe compound or anything at all? And no wise guy remarks with the nipple thing!!! :p

Any type of thread sealer will work fine. I use Permatex white teflon sealer, but have also used teflon tape and Indian Head gasket shellac. Pipe threads are tapered and designed to sort of seal them selves so it does no take much to get them sealed up. Teflon tape is nice if you want it to look "clean" because you can peel off whatever tape is left outside of the joint after you tighten it down. Just dont get carried away with it, a couple of wraps is all it takes.

Perfect...thanks Bill.

This is obviously for water lines, but it might be worth pointing out that it's not a good idea to use teflon tape on fuel lines. You'll shred the tape when you tighten the fitting, and you can end up with pieces of teflon tape in the carburetor. It's one of those "don't ask me how I know" things :)

Except from that, I use teflon tape on most fittings for the same reason Bill mentioned. Even if pipe thread is supposed to be self sealing, they're often a bit rough so some tape is cheap insurance.

After pulling the threads out of a water pump and an intake manifold I use a generous supply of antiseize on the threads on anything threading into aluminum. I started doing it this way on my new intake manifold and in 1300 miles of driving i've had no leaks from the intake or water pump. I disconnected my heater hoses and had to remove the fittings and replace them with plugs.

Bill's avice is excellent.
It really doesn't matter what's flowing through it.
What matters is the type of fitting when deciding what to use.

With any fitting you should not have anything at all on the first couple of threads to keep it out of the inside.

My old boss, a master plumber used to tell me that since pipe threads are tapered and self sealing all they really need is lubrication.

Everyone has their own favorites, I like permatex "Form A Gasket" or Indian Head gasket shellac myself.

Two words: Loctite PST